class Solution {
    int dx[4]={0,0,1,-1};
    int dy[4]={1,-1,0,0};
    int m,n;
public:
    void solve(vector<vector<char>>& board) {
        m=board.size(),n=board[0].size();
        for(int j=0;j<n;j++)
        {
            if(board[0][j]=='O')bfs(board,0,j);
            if(board[m-1][j]=='O')bfs(board,m-1,j);
        }
        for(int i=0;i<m;i++)
        {
            if(board[i][0]=='O')bfs(board,i,0);
            if(board[i][n-1]=='O')bfs(board,i,n-1);
        }
        for(int i=0;i<m;i++)
        {
            for(int j=0;j<n;j++)
            {
                if(board[i][j]=='O')board[i][j]='X';
                else if(board[i][j]=='.')board[i][j]='O';
            }
        }
    }
    void bfs(vector<vector<char>>& board,int i,int j)
    {
        queue<pair<int,int>> q;
        q.push({i,j});
        board[i][j]='.';
        while(q.size())
        {
            auto [a,b]=q.front();q.pop();
            for(int k=0;k<4;k++)
            {
                int x=a+dx[k],y=b+dy[k];
                if(x>=0 && x<m && y>=0 && y<n && board[x][y]=='O')
                {
                    q.push({x,y});
                    board[x][y]='.';
                }
            }
        }
    }

};
